Cardinals are chosen by the pope to serve as his principal assistants and advisers in the central administration of church affairs in one or more departments of the Roman Curia. Collectively, they form the College of Cardinals or the Sacred College. Canons 349-359 govern the makeup and responsibilities of the College.

Since 1059, Cardinals have been serving as exclusive electors of the Pope in a conclave during the Sede Vacante (when the Holy See becomes vacant). By Ingravescentem Aetetem (1971), Cardinals who have completed their 80th year of age can no longer take part in a papal election. Universi Dominici gregis (1996) and Normas nonnullas (2007) contain the latest laws governing a papal election.

The title of Cardinal, while symbolic of high honour, does not signify any extension of the powers of the holy orders. By the 1815 Congress of Vienna, all Cardinals have the rank and privileges equal to princes of royal birth; hence they are also known as the Princes of the Church.

Cardinalsin pectore are those who have been selected by the pope but whose name have not been disclosed usually because of political reasons. They have no title, rights or duties until such disclosure is made.